1. Technical Field of the Invention
The present invention relates to a heat treatment apparatus, a calibration method for temperature measuring system of the heat treatment apparatus, and a heat treatment system.
2. Description of the Related Art
A vertical heat treatment apparatus, which performs a batch-type process on semiconductor wafers (which will be hereinafter referred to as “wafer(s)”), is known as one of the heat treatment apparatuses that performs a heat treatment on the wafers in a semiconductor device fabricating process. When performing the heat treatment, many wafers are carried by a wafer boat at intervals in the vertical direction and loaded into a reaction tube where the heat treatment, such as CVD process or oxidation process, is applied on the wafers.
Temperatures of the wafers have a great influence on the results of heat treatment. For instance, in case of film-deposition by the CVD process, a film-thickness changes depending on the temperatures of wafers. Accordingly, the temperatures of wafers during the heat treatment have to be controlled precisely. To this end, an accurate temperature measurement is necessary.
In a single-wafer heat treatment apparatus, the wafer is mounted face-to-face on a wafer table called a “susceptor”. Accordingly, the temperature of the susceptor becomes generally equal to a temperature of the wafer mounted thereon. Thus, it is possible to obtain the temperature of the wafer with high accuracy by measuring the temperature of the susceptor via the use of a thermoelectric couple embedded therein. However, in the vertical heat treatment apparatus, where a plurality of wafers are held by the wafer boat to be simultaneously processed, a temperature sensor must be arranged remote from the wafers.
Therefore, in the midst of changing the temperature in the reaction tube, there exists a difference between the temperature detected by the temperature sensor and the actual temperatures of the wafers.
In order to measure the temperatures of the wafers with high accuracy, the temperature measurement has to be performed after the temperature in the reaction tube has been stabilized. This means a reduction in throughput of the apparatus.
In order to solve such a problem, there have been temperature measuring methods recently developed, taking the transitional response into consideration. U.S. Pat. No. 5,517,594, for example, discloses such method.
In the method disclosed therein, the temperature measurement is executed by using ARX model. The constant matrixes in the ARX model are determined, upon actual experiments, based on detection signals from thermoelectric couples arranged in the reaction tube, detection signals from thermoelectric couples directly attached to test wafers and electric power supplied to heaters.
However, this method involves the following problems. First, the use of wafer with the thermoelectric couple might cause metals of the thermoelectric couple to be dispersed into the reaction tube, thereby causing it to be contaminated. Therefore, it is not preferable that the manufacturer of the heat treatment apparatus performs such experiments on the product apparatus to be supplied to the user. In this view, it is possible to perform an experiment for one of the apparatuses manufactured with the same specifications, and apply the model determined in said one of the apparatuses on the other apparatuses. However, even when manufactured with the same specifications, some variation will exist. Furthermore, after using the apparatus for a long term, a periodic change in the condition of the apparatus occurs.
Since the above method cannot cope with these problems sufficiently, there is a possibility of insufficient accuracy in determining the temperature.